This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Surgical treatment of disabling, medication refractory tremor secondary to head trauma or multiple sclerosis MS has proven difficult than treatment of essential or parkinsonian tremors. There have been no prospective blinded studies to evaluate efficacy of surgical treatments for these tremor subtypes. We reported successful use of 2 ipsilateral thalamic DBS electrodes one at the ventralis intermedius nucleus/ventralis oralis posterior nucleus border VIM and one at the ventralis oralis anterior nucleus/ventralis oralis posterior nucleus border VO for treatment of 1 patient with severely disabling and medication refractory tremor secondary to head trauma. We have applied this technique effectively in 2 more patients with post-traumatic tremor, and 1 with tremor secondary to MS. Mechanisms for additive benefit from the 2nd DBS electrode remain uncertain;we suspect that stimulation of both pallidal and cerebellar circuits, along with increased volume of stimulation covering wider somatotopy associated with the 2nd stimulator underpin the observed positive effects. The safety, benefits, and side effects of this promising technique remain incompletely elucidated. We now propose to rigorously test clinical effectiveness of dual ipsilateral thalamic DBS, and to characterize safety, benefits and side effects of this procedure for treatment of refractory post-traumatic or MS-related tremors. The study will be prospective, blinded, and will compare VIM DBS to VO DBS, as well as each of the four possible DBS conditions VIM DBS on - VO DBS on, VIM DBS on - VO DBS off, VIM DBS off - VO DBS on, and VIM DBS off - VO DBS off.